Multistage centrifugal gas compressor



Sept. 3, 1963 s. F. FQGLEMAN ETAL 3,102,680

MULTISTAGE CENTRIFUGAL GAS COMPRESSOR Filed June 27, 1961 INVEN TOR. 5AME FbGLEA IAM, Gus A. FOGLEMAN JR.

HERBERT C. 5CHULZE ATTORNEY United States Patent 3,102,686 MULTISTAGECENTRIFUGAL GAS QOMPRESSOR Sam F. Fogleman, 4941 Mount Frissell Drive,San Diego, Calif., and Gus A. Fogleman, Jr., 3365 llnverness St,Riverside, Calif.

Filed June 27, 1961, Ser. No. 119,990

2 Claims. (Cl. 230-130) This invention relates generally to centrifugalgas or vapor compressors and particularly to devices in which the gasesre-enter the impeller in multiple stages from annular gas passages whichare disposed axially around the impeller shaft centerline.

The main objective of this invention is to provide an improved means ofinterstage labyrinth sealing between the multistage rotating impellerand the stationary casing.

Another objective of this invention is to provide an improved impellerstructural rigidity by means of spacer rings interposed betweenadjoining stages of the multistage impeller.

Re-entry type centrifugal compressors of the adjacent parallel flow typein the past have not been commonly marketed, because manufacturing costswere too high to obtain reasonable efiiciencies. To achieve reasonableefiiciencies interstage gas leakage must be minimized particularly atthe outer periphery of the impeller. Since labyrinth seal leakage variesdirectly with the diameter of the seal it is important to minimize thediameter at the labyrinth seal interface.

The impeller of this type compressor in vicinity of the second andhigher stages is conventionally supported in a cantilever manner fromthe main backplate of the first stage impeller. A rigid, reinforcedimpeller construction is desirable to allow the impeller stages to bebolted or riveted together so as to minimize axial wobble of thecomponents as well as to minimize radial displacement of the componentsrelative to shaft centerline. This rigid, reinforced construction of thecantilever supported impeller resists the distortion effects ofcentrifugal force and allows minimum vibration plus confinement of theimpeller to a more concentric shape which allows the labyrinth sealradial clearances to be held to a minimum with reduced labyrinth sealleakage. Labyrinth seal leakage varies approximately as the second powerof thisinterface radial clearance.

Freon refrigerants when compressed exhibit a much higher degree ofcompressibility than air or monatomic gases. The machine to be describedherein will be used primarily for compressing Freon refrigerants and assuch the axial impeller vane width at impeller tip is considerablyreduced in relation to vane axial width near the inlet with gas passagesthat are gradually tapered to narrower axial widths as the gas flowprogresses radially outward. These tapered gas passages for Freons aremore pronounced than in air compressors and relatively large axial gapsare inherently required between adjacent stage enclosures. An objectiveof this invention is to utilize these axial gaps as locations forinterstage labyrinth seals and for impeller reinforcing spacer rings.

The foregoing and other objects and advantages of this invention will beclear to those skilled in the art upon reading the followingspecification in connection with the attached drawings, in which:

FIGURE -1 is a perspective view of the compressor representing apreferred embodiment of the invention; and

FIGURE 2 is a vertical sectional view.

Referring to the drawings in which a preferred embodiment of theinvention is disclosed, a conventional vertically positioned electricdriving motor is referred to generally as M. Gas leakage along the motordrive shaft 10 is restricted by a labyrinth seal 12 that is secured to abottom or base 14 that flares outwardly at 16 into a vertically disposedcylindrical compressor casing 18. The casing bottom or base 14 isapertured at 20 to receive the motor shaft 10. The casing 18 isgradually curved at 22 to merge into a flat section 24 projecting fromthe flared portion 16.

The compressor outer casing 18 has a cover 26 connected thereto by meansof a plurality of bolts or attachment screws 27. A low pressure gasinlet pipe 28 projects through and is secured centrally to the cover 26.The connection of the cover 26 and inlet pipe 28 forms a graduallycurved inner surface 29. The inlet pipe 2.8 depends downwardly to apoint immediately adjacent a multistage centrifugal impeller, later tobe described. The cover 26 also has secured and depending therethroughone or more high pressure gas outlet pipes 30.

A first stage impeller back plate 32 has a hub 34 keyed at 36 on themotor shaft .10. Secured to the back plate 32 are a multiple of firststage impeller vanes 38 projecting upwardly and diagonally outwardtherefrom. The multiple vanes 38 taper gradually toward the outerperiphery of the backplate 32. A bell-shaped stage dividing member 40 issecured to and overlies the multiple impeller vanes 38. The inner upperedges of the central opening of the first division bell 40 have sealseating surfaces 42 that are either seated or in close proximity tocoinciding surfaces 44- on a labyrinth seal ring 46 secured about thelower end of the lower pressure inlet pipe 28. The division bell 40 isgradually and concentrically curved at 48 into a gradual downward taperto ward the outer periphery of the first stage back plate 32 and uponthe similarly tapered multiple vanes 38. A first stage outer seal seatring 50 having sealing surfaces 52 is secured upon and adjacent theouter periphery of the first division bell 40. A second stage back plate54 overlies the division bell 4G and is secured inwardly thereto at 56.The back plate 54 is supported on as well as attached at 58 to the firststage outer labyrinth seal ring 50.

The high pressure gases expelled from the constricted bladed peripheralopenings 59 in the first stage multiple impeller are projected radiallyoutward toward the inher surface of the outer casing 18. An annularfirst stage diffusion chamber 60 is provided to contain the highpressure gases by means of a disc-shaped outer partition 62 within andspaced from the outer casing 18. The partition 62 is connected forassembly purposes in one plural manner designated 64 to an inner andupper circular disc partition 66 that is supported at 6-7 by one or bothof the high pressure outlet pipes 30. The partition 62 is formed with aflat lower surface 68 that is fixedly sustained immediately adjacent therapidly rotating peripheral edge of the second stage back plate 54. Theflat surface 68 is curved concentrically and. gradually at 70 to mergeinto vertical circular sides of the casing 62'. The vertical sides arecurved gradually at 74 to merge with and be connected in the pluralbolted rnanner 64 to an outer annular peripheral edge '78 of the innercircular partition 66. The partition 66 is curved gradually at 79. Thecompletely open concentric diffuser chamber 60 is formed to circulatethe high pressure gas or vapor from the first stage of the multiplere-entry compressor generally designated C.

An outer stationary labyrinth seal ring is secured to the under fiatlower surface 68 of the outer partition or disc 62. The seal ring 80 hassealing surfaces 82 coinciding in conventional manner with the adjacentsurfaces 52 on the first stage impeller outer labyrinth seal ring 50.The labyrinth sealing means heretofore described restricts anyinterstage gas leaks. The annular first stage difiusion chamber 60directs the highside vapors radially outward, upward and inward to thesecond stage inlet annular space between Walls of pipe 28. The gas flowis uninterrupted in a gradually curved manner until it re-enters abell-shaped second stage impeller inlet 8 60f the second stage of themultistage compressor C.

The impeller outer labyrinth seal ring 50 is shown as as a separatedpart. An alternate type construction would be to have the configurationof the labyrinth seal ring 50 cast or formed as an integral part ofeither the first division bell 40, or as an integral part of the secondstage back plate 54.

The second stage back plate 54 has a multiple of second stage impellervanes 90 thereon which are radially disposed and taper outwardly in amanner similar to the first stage impeller vanes 38. The second stagevanes 90, however, are somewhat smaller than the vanes 38. A secondstage division bell 92 overlies and is secured on the upper edges of thesecond stage impeller vanes 99. The bell 92 tapers outwardly and aseries of inner edges 94 on an open centering ring 96 provide sealingsurfaces with coinciding portions 98 on a second stage stationarylabyrinth seal ring 100 on the lower peripheral edge of the previouslydescribed upper and inner annularly disposed partition or disc 66. Thebell 92 is gradually curved at 102 to provide the gas re-entry bellshaped opening 86. The first and second stage bells, 40' and 92respectively, are curved and tapered in parallel planes to form smoothcompressor re-entry gas passages or diffusion chamber 103. The secondstage impeller compresses the gases through impeller passages (which areslightly reduced in size and area. This second stage impeller size andarea reduction is required to accommodate a gas which is compressed ormore dense than that flowing in the first stage impeller. A third stageimpeller back plate 104 is secured at its inner edge 1% to the bell 92and at its outer end is attached upon a second stage outer labwinthsealing ring 108. A second concentric disc or partition 110 positionedinwardly of the first outer partition 62 has its upper inner edge 112bolted in a plural manner at 114 to the outer peripheral edge .116 of asecond upper and inner disc shaped partition 118. The disc 118 issecured to and supported at 120 by one of the high pressure outlets 30.The second partition 110 has a lower flat side 122 and an inner circularedge 124 assumes a stationary position immediately adjacent the rotatingperipheral edge of the back plate 104. A stationary circular sealingring 126 is attached to the under side of the flat surface 122 and theinner edges 128 thereof coincide in the usual manner with the seatingsurfaces on the second stage labyrinth outer seal ring 108. As statedbefore, the labyrinth sealing devices restrict interstage gas leakage.

The movement of the compressor vapors in the second stage of thecompressor C is exactly the same as described for the first stage. Thethird stage impeller back plate 104 has also a series of multipleimpeller blades 136 thereon which are somewhat smaller but formed inexactly the same manner as first and second stage vanes 38 and 90respectively. A third stage division bell 13 8 smaller but of largerinside diameter and formed the same as the first and second stage bells,has an inner central rim 140 that also has sealing surfaces 142 thereon.The upper and inner second stage disclike partition 118 has a stationarylabyrinth sealing ring 144 on its lower edge that engages the sealingsurfaces 142. An annular open faced disc 146 of torous or doughnut shapeis supported from one of the high pressure outlets 30. The disc .146 hasa third stationary labyrinth seal 148 secured to its lower side forsealing surface engagement with a third stage outer labyrinth seal 150secured adjacent the outer edge of the third stage bell 138. A diffusionconduit 152 connects the third stage higher pressure impeller blades 136with an annular chamber 154 that has communication with one or more ofthe high' pressure outlets 31].

The impeller outer labyrinth seal ring 108 is shown as a separated part.An alternate type construction would be to have the configuration of thelabyrinth seal ring 10 8 cast or formed as an integral part of eitherthe second stage division bell 92, or as an integral part of the thirdstage backplate 104.

Although the drawings disclose a triple stage re-entry type compressor,it is contemplated that two or more stages may be used depending uponrequirements of pressure and volume flowing. Fabrication of an eightstage compressor of the present type would merely result in reduction ofimpeller diameter and size of the compressor housing.

As far as the operation is concerned, the impeller output and return ofgases thereto through the three stages has been described in detail. Theparallel flow of gases of each stage within the impeller and casing haveonly the tin partitions or division members between the parallel flowssuch that the labyrinth seals described and as shown are located outsidethe main gas passages to minimize the main gas flow resistance.

The tapered gas passages enclosing the impeller vanes necessitate gapsbetween adjoining impeller stages near the outer periphery of theimpeller. These gaps are blocked-oil by the labyrinth seal rings 50 and108 and consequently the labyrinth seals between 50 and 82 and between108 and 128 are located outside the main gas flows. The gap spacerequired between impeller stages allows the labyrinth seal rings 50 and108 to occupy some axial length. This inherent axial length of 50 and108 is desirable for use as generous labyrinth sealing surfaces. Thelabyrinth seal rings 50 and 108 serve as structural reinforcement toprevent axial wobble of the division bells 40 and 92 and to the impellerback plates 54 and 104.

tWhile the embodiment of our invention shown herein is fully capable ofperforming the objects and advantages desired, it will be apparent tothose skilled in the art that numerous modifications may be made withoutdeparting from the inventive concept disclosed herein. It is notintended that this invention be limited by the embodiments disclosed butonly as necessary in accordance with the appended claims.

We claim: 1. In a multistage centrifugal compressor, comprising: animpeller having all parallel gas flow passages for each impeller stage,said passages separately enclosed by partitions, said partition ofsubsequent stages axially separated from' each other on the outerperiphery of the impeller,

rotating spacer rings disposed annularly on a centerline common with theimpeller centerline and disposed at a diameter less than impelleroutside diameter and disposed axially between and abutting to two ofsaid partitions of two subsequent impeller stages,

void spaces in the impeller between sub-sequent impeller stages, saidvoid impeller spaces defined on the outer periphery by the outsidediameter of the impeller, said void spaces defined on the insidediameter \by said spacer rings, said void spaces defined axially on thesides by two partitions of two subsequent impeller stages,

labyrinth seal seating surfaces on the outer periphery of said spacerrings, and casing partitions with annular labyrinth packing locatedwithin the afore mentioned impeller void spaces, said larbyrinth packingalso located in proximity to and spaced therefrom, said labyrinth sealseating surfaces of said spacer rings, for the purpose of minimizinginterstage gas leakage.

2. A device as claimed in claim 1 wherein a multistage impeller with gaspassages having a large axial width near impeller gas inlet and arelatively smaller axial width near impeller gas outlet,

partitions enclosing gas passages, said passages to have a graduallydownward taper toward the outer periphery, said partitions to define thedifferences in said axial widths of impeller inlet and impeller outlet,labyrinth packing located between tapered partitions of subsequentimpeller stages, said packing occupying an axial width approximatelyequal to the difierence between the axial widths of said impeller gasinlet and said gas outlet, whereby the assembly of the impeller withtapered gas passages does not require any increase in overall impelleraxial width to provide axial space for the labyrinth packing.

References Cited in the file of this patent UNITED STATES PATENTSAnderson Sept. 4, 1917 Frame July 8, 1919 FOREIGN PATENTS SwitzerlandApr. 16, 1921 Great Bn'tain Jan. 22, 1931 Germany Dec. 17, 1921

1. IN A MULTISTAGE CENTRIFUGAL COMPRESSOR, COMPRISING: AN IMPELLERHAVING ALL PARALLEL GAS FLOW PASSAGES FOR EACH IMPELLER STAGE, SAIDPASSAGES SEPARATELY ENCLOSED BY PARTITIONS, SAID PARTITION OF SUBSEQUENTSTAGES AXIALLY SEPARATED FROM EACH OTHER ON THE OUTER PERIPHERY OF THEIMPELLER, ROTATING SPACER RINGS DISPOSED ANNULARLY ON A CENTERLINECOMMON WITH THE IMPELLER CENTERLINE AND DISPOSED AT A DIAMETER LESS THANIMPELLER OUTSIDE DIAMETER AND DISPOSED AXIALLY BETWEEN AND ABUTTING TOTWO OF SAID PARTITIONS OF TWO SUBSEQUENT IMPELLER STAGES, VOID SPACES INTHE IMPELLER BETWEEN SUBSEQUENT IMPELLER STAGES, SAID VOID IMPELLERSPACES DEFINED ON THE OUTER PERIPHERY BY THE OUTSIDE DIAMETER OF THEIMPELLER, SAID VOID SPACES DEFINED ON THE INSIDE DIAMETER BY SAID SPACERRINGS, SAID VOID SPACES DEFINED AXIALLY ON THE SIDES BY TWO PARTITIONSOF TWO SUBSEQUENT IMPELLER STAGES, LABYRINTH SEAL SEATING SURFACES ONTHE OUTER PERIPHERY OF SAID SPACER RINGS, AND CASING PARTITIONS WITHANNULAR LABYRINTH PACKING LOCATED WITHIN THE AFOREMENTIONED IMPELLERVOID SPACES, SAID LABYRINTH PACKING ALSO LOCATED IN PROXIMITY TO ANDSPACED THEREFROM, SAID LABYRINTH SEAL SEATING SURFACES OF SAID SPACERRINGS, FOR THE PURPOSE OF MINIMIZING INTERSTAGE GAS LEAKAGE.